1. Field of the Invention
This invention relates to a particle cluster, a composite structure formation method, and a formation system, and more particularly to a particle cluster, a composite structure formation method, and a formation system for aerosol deposition method by which an aerosol with fine particles of a brittle material dispersed in a gas is sprayed onto a substrate to form a structure made of the fine particles on the substrate.
2. Background Art
The “aerosol deposition method” is one of the methods for forming a structure made of a brittle material on the surface of a substrate (e.g., Patent Documents 1 to 3). In this method, an aerosol in which fine particles including a brittle material are dispersed in a gas is sprayed from a discharge port toward the substrate to collide the fine particles with the metal, glass, ceramic, or plastic substrate, deforming or crushing the brittle material fine particles by the impact of this collision to join them together, so that a film-like structure made of the fine particles is directly formed on the substrate. This method can form a film-like structure at normal temperature without requiring any specific heating means and the like, and can provide a film-like structure having a mechanical strength which is at least comparable to that of a sintered body. Furthermore, the condition for colliding the fine particles as well as the shape, composition and the like of the fine particles can be controlled to diversely vary the density, mechanical strength, electrical characteristics and the like of the structure.
To form a large-area film-like structure by this aerosol deposition method, fine particles need to be continuously supplied for a prescribed period of time. In particular, in the case where a high film thickness accuracy is required, it is desired that the supply quantity of fine particles be constantly stable.
However, as disclosed in Patent Document 1, if aerosolation is allowed to occur in a storage mechanism storing fine particles of a raw material, the capacity of the storage mechanism needs to be far larger than the volume of fine particles to secure the capacity for aerosolation, which may require a large-scale apparatus. Furthermore, when a large quantity of fine particles are stored, the state of the fine particles may change over time, leaving a problem with stable supply of the aerosol.
In this context, as disclosed in Patent Documents 2 and 3, a technique is proposed in which the storage mechanism for storing fine particles is separated from the aerosolation mechanism for mixing the fine particles with a gas to produce an aerosol, and the fine particles are transported from the storage mechanism to the aerosolation mechanism by required amount.
However, in the case where submicron or smaller fine particles are used as primary particles, because of high viscosity and adhesiveness, the problems of adhesion, stacking and the like to the wall surface are likely to occur inside the storage mechanism and in the process of transport from the storage mechanism to the aerosolation mechanism, which may make it difficult to transport reliably. For instance, fine particles become likely to aggregate due to agitation and migration inside the storage mechanism and change their fluidity. Eventually, stacking occurs inside the storage mechanism and prevents migration of powder to the aerosolation mechanism, and hence the quantitativeness of the supply quantity is lost. Furthermore, adhesion occurring inside the storage mechanism may also yield adverse effects, such as failing to achieve powder usage as planned.
Furthermore, the fine particle, or the group of fine particles split in a prescribed size and shape, may be nonuniform in shape and density when carried out of the storage mechanism. In this case, even using an aerosolation mechanism having a prescribed disaggregation capability, it may be difficult to generate an aerosol with a constantly stable fine particle concentration. Furthermore, also in the case where the group of fine particles split in a prescribed size and shape changes in shape or density during the transport process, it may be difficult to accurately control the fine particle concentration in the aerosol.    Patent Document 1: Japanese Patent No. 3348154    Patent Document 2: JP-A-2006-200013    Patent Document 3: JP-A-2006-233334